In general, as shown in a prior art beverage can as illustrated in FIG. 1A, a closure 2 is formed by a scored line 1 which has a deepness smaller than the thickness of an upper portion of a beverage can at one side of the upper surface of the can. A lever 3 is fixed to an upper central portion of the can. In this case, the scored line is not formed near the portion where the lever 3 is installed (that is, a portion near the upper central portion of the can at the circumference of the closure 2) so that one side of the closure 2 is not separated from the upper surface of the can. In addition, a tip of the lever 3 extends from one side of the closure 2 and is fixed to the one side of the closure 2.
Therefore, when a user holds a rear end of the lever 3 and then lifts up the lever 3, the tip of the lever 3 presses an upper surface of the closure 2 downward. As a result, the circumference of the closure 2 is cut out from the upper surface of the can along the scored line 1 and bent downward to form a discharge port (shown, for example, in FIG. 2A).
In the beverage cans having the above structure, the closure 2 is connected to the upper surface of the beverage can and is not separated from the upper surface of the beverage can even though the beverage can is opened. As a result, the beverage cans may be easily recycled and widely used.
However, once the closure 2 of such beverage can is opened, the opening cannot be closed and the beverage cannot be securely preserved. Therefore, in order to solve the above problem, as illustrated in FIG. 1B, an auxiliary closure for a beverage can, which has a quadruple sealing structure, is disclosed in Korean Patent No. 10-1199690 titled “Spare stopper with quadruple air tight structure for beverage can” filed on May 17, 2012.
FIG. 1B illustrates a bottom perspective view illustrating an auxiliary closure for a beverage can, according to the prior art.
Referring to FIGS. 1A and 1B, according to the prior art, the auxiliary closure for the beverage can in which the closure 2 is formed by a scored line at one side of an upper surface of the beverage can. The lever 3 is fixed onto the upper central portion, and an extending portion 4 having a narrowed diameter portion formed on an outer circumferential surface extends upward from an upper circumferential surface, and a concave groove 5 having a concave ring shape is formed downward so as to be positioned in the extending portion 4 such that when the closure 2 is pushed downward by using the lever 3, the circumferential surface of the closure 2 is cut out from the upper surface of the can to form a discharge port. The beverage can includes a support portion 6 having a wide circular plate shape, an outer extending end tube 7 (which extends downward from a lower circumferential surface of the support portion 6), a catching project 7a (which is caught by the narrowed diameter portion at an inner circumferential surface thereof), an inner extending end tube 8 (which has a smaller diameter than the outer extending end tube 7) extends downward to be concentric with the outer extending end tube 8 and has a lower end inserted into the concave groove 5, and a sealing member 9 (which is made of an elastic material) fixed at a lower side of a support portion 41 and seals the discharge port by being tightly attached to an upper surface around the discharge port.
However, the auxiliary closure in the prior art is configured to cover the upper surface of the beverage can so that the member 9 blocks the discharge port 2a. But only when the sealing member 9 is inserted between the lever 3 and the upper surface of the can, the discharge port may be securely blocked. In addition, when the upper surface of the can is covered without checking that the sealing member 9 is inserted between the lever 3 and the upper surface of the beverage can, a beverage leaks through the discharge port 2a. 
Further, according to the prior art in Korean Patent No. 10-1199690, a spiral groove is formed on an outer surface of the outer extending end tube (an inner cap) and a sealed cover (an outer cap) is formed having a ring shape at the outside of the outer extending end tube. For example, when the outer cap (similar to a male spiral screw) slide down on the inner cap (similar to a female spiral screw), forces are exerted towards inner direction for squeezing the inner cap in order to air-tightly seal the upper side of the can. However, significant manual work is required for the spiral groove, and as a result, productivity is decreased. Thus, there remains a need for a beverage can with a new structure.